JP4293109B2 - Method for producing silicon carbide single crystal - Google Patents

Description

  The present invention relates to a method for producing a silicon carbide single crystal.

  Since silicon carbide single crystal has characteristics of high breakdown voltage and high electron mobility, it is expected as a semiconductor substrate for power devices. A single crystal growth method generally called a sublimation method (improved Rayleigh method) is used for the silicon carbide single crystal. In the improved Rayleigh method, a silicon carbide raw material is inserted into a graphite crucible, a seed crystal is disposed so as to face the raw material portion, and the raw material portion is heated to 2200 to 2400 ° C. to generate sublimation gas. A silicon carbide single crystal is grown by recrystallizing into a seed crystal cooled to several tens to several hundreds of degrees C. from the part. In this improved Rayleigh method, the amount of silicon carbide raw material decreases as the silicon carbide single crystal grows, so there is a limit to the amount by which the crystal can grow longer. Even if the raw material is added during the growth, the concentration of sublimation gas in the crucible is increased if the raw material is added during the growth because the Si / C ratio sublimates when SiC sublimates. Fluctuates and becomes an obstacle to the continuous production of crystals of high quality.

  On the other hand, Patent Document 1 discloses a technique for epitaxially growing silicon carbide by CVD. FIG. 10 is a schematic sectional view of a manufacturing apparatus using this technique. As shown in FIG. 10, a cylindrical susceptor 101 is disposed near the center of the cylindrical case 100. The susceptor 101 is made of high purity graphite or the like. A seed crystal (silicon carbide single crystal substrate) 102 is arranged on the upper end surface of susceptor 101. A heating means 103 for heating the gas in the susceptor 101 is disposed at a position corresponding to the outer periphery of the susceptor 101 outside the case 100. The periphery of the susceptor 101 is filled with porous graphite 104 which is a heat insulating material. A funnel-shaped passage 105 is formed by the heat insulating material 104 at the lower end of the susceptor 101. A mixed gas introduction pipe 106 for supplying a mixed gas containing Si and C necessary for the growth of the silicon carbide single crystal is disposed at the lower end of the case 100. Further, a passage 107 through which the mixed gas is exhausted is formed at the upper end surface of the susceptor 101, and a gas passage 108 connected to the outside of the case 100 is formed at the upper portion of the case 100. In the manufacturing apparatus having such a configuration, the mixed gas supplied from the mixed gas introduction pipe 106 moves into the susceptor 101 through the passage 105 formed by the heat insulating material 104, and the mixed gas is heated by the heating means 103. A silicon carbide single crystal is epitaxially grown from seed crystal 102. The remaining mixed gas passes through the passage 107 on the upper end surface of the susceptor 101 and is exhausted through the passage 108 formed in the upper portion of the case 100. Also, during the epitaxial growth of silicon carbide single crystal, unlike the conventional CVD technique, the susceptor and substrate temperature are raised to a temperature normally used for growing a boule body by the sublimation technique. Thus, the etching of the object grown on the seed crystal 102 with hydrogen or other etching gas is considerably enhanced at these high temperatures, and the polycrystalline region, ie, the relatively low quality region is a single crystal region, That is, the etching is performed more rapidly than the high quality region, and as a result, a high quality crystal can be grown.

However, in the production of a silicon carbide single crystal by this CVD, when the susceptor 101 is heated to a high temperature at which bulk crystal growth is possible, the required partial pressure of the raw material varies depending on the temperature of the seed crystal. A gas containing Si and C having a partial pressure of a raw material is calculated and introduced. However, in this method, unintentional fluctuations in the gas flow rate setting, such as changes in the crystal surface temperature due to changes in the gas flow rate, and changes in the temperature distribution during temperature rise transients, are optimal for the temperature of the seed crystal during the temperature rise process. It is extremely difficult to raise the temperature without generating defects by supplying a simple raw material. As another method, there is a method of heating so as not to cause crystal growth using an inert gas. However, even if argon, helium, etc. are used as the inert gas, sublimation from the seed crystal is actually Si, C. Since it occurs at different ratios, carbonization occurs due to Si loss on the surface of the seed crystal, and a high-quality crystal cannot be produced thereon. Further, by introducing the source gas and the carrier gas into the susceptor without being linked with the temperature control, the temperature is lowered in the susceptor due to the introduction of the gas, the growth conditions are removed, and crystal defects are introduced. Once a crystal defect occurs on the crystal surface, the crystal on it cannot be formed with high quality from the principle of epitaxial growth.
Japanese National Patent Publication No. 11-508531

  The present invention has been made under such a background, and an object thereof is to provide a method for producing a silicon carbide single crystal capable of producing a high-quality silicon carbide single crystal by a novel method. is there.

  The method for producing a silicon carbide single crystal according to claim 1 increases the growth atmosphere temperature to the crystal growth temperature so that the crystal grows from the silicon carbide seed crystal by supplying a raw material gas to the silicon carbide seed crystal. A first step of heating and removing the carbon grown from at least the silicon carbide seed crystal by an etching gas supplied to the silicon carbide seed crystal in addition to the raw material gas while maintaining the growth atmosphere temperature at the crystal growth temperature. The second step of exposing the clean surface of the silicon seed crystal, and gradually reducing the etching gas supplied in addition to the raw material gas while maintaining the growth atmosphere temperature at the crystal growth temperature. And a third step of starting crystal growth from the clean surface. Therefore, by etching until the clean surface of the seed crystal is exposed by the etching gas after the temperature rise is completed and high quality growth can be started, the crystal defects caused in the early stage of growth caused by the temperature rise process A defect can be eliminated and a high quality silicon carbide single crystal can be manufactured.

  Here, as described in claim 2, in the method for manufacturing a silicon carbide single crystal according to claim 1, in the first step, the gas used as a raw material in a state where the surface of the silicon carbide seed crystal is a clean surface. It is preferable that the crystal grows from the silicon carbide seed crystal by supplying.

  The method for producing a silicon carbide single crystal according to claim 3, wherein the surface of the silicon carbide seed crystal is etched with an etching gas supplied to the silicon carbide seed crystal in addition to the gas as a raw material to expose the clean surface. A first step of raising the atmospheric temperature to the crystal growth temperature, and gradually reducing the etching gas supplied in addition to the raw material gas while maintaining the growth atmospheric temperature at the crystal growth temperature. And a second step of starting crystal growth from the clean surface of the crystal. Therefore, since the etching gas is supplied in addition to the gas used as a raw material when the temperature is raised to etch the surface of the seed crystal and expose the clean surface, a high-quality silicon carbide single crystal can be manufactured.

  According to the method for manufacturing a silicon carbide single crystal according to claim 4, in the method for manufacturing a silicon carbide single crystal according to any one of claims 1 to 3, the etching gas when the etching gas is gradually reduced. By gradually changing the flow rate of the gas so that the change in the ambient temperature is 5 ° C./min or less, a high-quality silicon carbide single crystal can be obtained without removing the optimum growth conditions when shifting from etching to growth. It becomes possible to grow.

  According to the method for producing a silicon carbide single crystal according to claim 5, in the method for producing a silicon carbide single crystal according to any one of claims 1, 2, and 4, at least carbonization with an etching gas in the second step. When removing the crystal grown from the silicon seed crystal to expose the clean surface of the silicon carbide seed crystal, at least one of the thickness of the silicon carbide seed crystal and the thickness of the crystal grown from the silicon carbide seed crystal is expressed as X By controlling the etching amount while measuring using a wire, it is possible to prevent the disappearance of the seed crystal due to excessive etching and the insufficient etching amount due to insufficient supply of the etching gas, and the quality of the initial stage of growth with good reproducibility. High quality can be achieved.

  According to the method for manufacturing a silicon carbide single crystal according to claim 6, in the method for manufacturing a silicon carbide single crystal according to claim 3 or 4, the surface of the silicon carbide seed crystal is etched with an etching gas in the first step. By controlling the etching amount while measuring the thickness of the silicon carbide seed crystal using X-rays, when the temperature of the growth atmosphere is raised to the crystal growth temperature while exposing the clean surface, it is caused by excessive etching. It is possible to prevent the disappearance of the seed crystal and the insufficient etching amount due to insufficient supply of the etching gas, and the quality at the initial stage of growth can be improved with high reproducibility.

  According to the method for manufacturing a silicon carbide single crystal according to claim 7, in the method for manufacturing a silicon carbide single crystal according to any one of claims 1 to 6, to the silicon carbide seed crystal in a space to be heated. In the etching gas supply passage, a heat storage member that flows in contact with the etching gas is provided, and the heat storage member makes it difficult to change the ambient temperature when the amount of etching gas is reduced. Therefore, it is preferable to grow a high-quality silicon carbide single crystal.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, the schematic cross section of the manufacturing apparatus of the silicon carbide single crystal in this embodiment is shown.

  In FIG. 1, the apparatus is provided with a vacuum vessel 1 and a cylindrical vessel body 2 is arranged in an upright state. That is, the opening portions at both ends of the container body 2 are fixed in a state where they are positioned vertically. The container body 2 is made of, for example, quartz. The upper surface opening of the container body 2 is closed by an upper lid member (flange) 3, and the lower surface opening of the container body 2 is closed by a lower lid member (flange) 4.

  Inside the vacuum vessel 1, a cylindrical heat insulating material 5 is arranged along the inner wall of the vessel body 2. Inside the heat insulating material 5, a cylindrical reaction vessel 6 is arranged along the inner wall of the heat insulating material 5. The internal space of the reaction vessel 6 becomes a reaction chamber (crystal growth chamber). The upper surface of the reaction vessel 6 is closed and the lower surface is opened. A silicon carbide seed crystal (silicon carbide single crystal substrate) 7 is disposed facing downward in the upper part of reaction container 6, specifically, on the ceiling surface in reaction container 6. With respect to the heat insulating material 5 and the reaction vessel 6, the heat insulating material 5 is arranged at a predetermined interval on the side surface and the upper surface of the reaction vessel 6.

  As a material for the reaction vessel 6, for example, high-purity graphite that can withstand high temperatures (about 2400 ° C.) can be used. By using such high purity graphite, it is possible to reduce the generation of impurities from the heated reaction vessel 6 and the incorporation of impurities into the crystal during crystal growth.

  A concave portion 8 is formed in a central portion of the lower lid member (flange) 4 so as to protrude downward. The inner side of the recess 8 serves as a storage chamber R1 for storing foreign matter generated in the vacuum vessel 1. A mixed gas introduction pipe 9 is formed on the bottom surface of the recess 8, and the mixed gas introduction pipe 9 extends in the vertical direction. The upper end side of the mixed gas introduction tube 9 extends inside the vacuum vessel 1, and the mixed gas introduction tube 10 extends upward from the upper end of the mixed gas introduction tube 9. The mixed gas is introduced into the vacuum vessel 1 from the outside of the vacuum vessel 1 through the mixed gas introduction tubes 9 and 10. This mixed gas is a mixture of a raw material gas, a carrier gas, and an etching gas, and the mixing ratio of these gases can be adjusted. Specifically, monosilane (a gas containing Si) and propane (a gas containing C) are used as raw materials. Moreover, argon gas or helium gas is used as carrier gas. Further, hydrogen gas is used as an etching gas.

  A bottomed cylindrical member 11 is connected and supported at the upper end of the mixed gas introduction pipe 10. The bottomed cylindrical member 11 is arranged along the inner wall of the reaction vessel 6 inside the reaction vessel 6. The inside of the mixed gas introduction pipe 10 and the inside of the bottomed cylindrical member 11 communicate with each other, and the gas introduced into the mixed gas introduction pipes 9 and 10 is guided to the inside of the bottomed cylindrical member 11. The upper surface of the bottomed cylindrical material 11 is open, and the gas that has passed through the bottomed cylindrical material 11 travels toward the silicon carbide seed crystal 7. Further, this gas flow reverses on the ceiling surface of the reaction vessel 6, moves downward along the side wall of the reaction vessel 6, and escapes to the outside of the reaction vessel 6 through the through hole 6 a on the lower surface of the reaction vessel 6.

  In this way, the mixed gas introduction pipes 9 and 10 and the bottomed cylindrical material 11 are extended from the lower side of the reaction vessel 6 toward the silicon carbide seed crystal 7 in the reaction vessel 6, and on the surface of the silicon carbide seed crystal 7. A mixed gas (monosilane, propane, carrier gas, and etching gas) can be supplied.

  In addition, a heat storage member 12 is disposed in a gas passage directly above the gas introduction pipe 10 inside the bottomed cylindrical member 11 so as to be separated from the side wall and the bottom surface of the bottomed cylindrical member 11. The gas guided from the mixed gas introduction pipe 10 to the inside of the bottomed cylindrical member 11 hits (contacts) the heat storage member 12 and then moves toward the upper seed crystal 7. The heat storage member 12 as a temperature change prevention member has an atmosphere in which the introduced gas can easily maintain a constant temperature when the flow rate of the gas (raw material gas, carrier gas, etching gas) introduced by the gas introduction pipes 9 and 10 changes. This is to prevent a crystal defect from occurring by suppressing a temperature change (abrupt temperature change in the reaction vessel 6). It is preferable that the heat storage member 12 has a large heat capacity, and the maximum size that can enter the bottomed cylindrical material 11 is preferable.

The lower lid member (flange) 4, the concave portion 8, and the mixed gas introduction pipe 9 are integrated, and are made of, for example, a stainless steel plate material (SUS material).
An exhaust pipe 13 is connected to the side surface of the aforementioned recess 8 and the exhaust pipe 13 communicates with the storage chamber R1. An exhaust pump 15 is connected to the exhaust pipe 13 via a particle collector 14. The gas in the vacuum vessel 1 is discharged to the outside of the vacuum vessel 1 by the exhaust pump 15. At this time, the particle collector 14 captures foreign matters such as particles in the gas.

  On the other hand, an inert gas introduction pipe 16 is formed at the center of the upper lid member (flange) 3 described above. The lower end of the inert gas introduction pipe 16 extends to the notch 5 a in the heat insulating material 5 in the vacuum vessel 1. An inert gas (for example, argon gas) is introduced from the inert gas introduction pipe 16 and moves downward from the upper surface of the reaction vessel 6 through the side surface in the vacuum vessel 1. That is, an inert gas flows downward from the vicinity of the center of the upper lid member 3 through the inert gas introduction pipe 16, and flows downward around the reaction vessel 6 through the periphery of the reaction vessel 6. As described above, an inert gas is introduced into the reaction vessel 6 from above the reaction vessel 6 in the vacuum vessel 1, and an air flow that directs the gas (foreign matter) in the reaction vessel 6 to the outside of the vacuum vessel 1 through the through holes 6 a. Made. The upper lid member (flange) 3 and the inert gas introduction pipe 16 are integrated, and are made of, for example, a stainless steel plate material (SUS material).

  A heating coil (RF coil) 17 as a heating means is wound around the outer peripheral portion of the vacuum vessel 1 in the vessel body 2. The heating coil 17 includes an upper coil 17a and a lower coil 17b. The upper coil 17a can heat the upper portion of the reaction vessel 6, and the lower coil 17b can heat the lower portion of the reaction vessel 6. Moreover, the frequency of the alternating current applied to each coil 17a, 17b is different, and the temperature of the upper part and the lower part of the reaction vessel 6 can be controlled independently. Specifically, heating coil 17 (upper coil 17a, lower coil 17b) heats the portion where through hole 6a is formed in reaction vessel 6 to a higher temperature than silicon carbide seed crystal 7.

The gas introduced into the reaction vessel 6 is heated in the reaction vessel 6, and part of the gas is crystallized in the silicon carbide seed crystal 7, and the unreacted gas flows to the lower side of the reaction vessel 6.
The X-ray source 18 and the camera 19 are arranged so as to face each other outside the heating coil 17, and the upper part (mainly the location where the seed crystal 7 is arranged and below it) from the X-ray source 18 in the reaction vessel 6. An X-ray image is captured by the camera 19 while being irradiated with X-rays. Thereby, the thickness of the silicon carbide seed crystal 7 and the thickness of the crystal grown from the silicon carbide seed crystal 7 can be measured.

Next, a method for producing a silicon carbide single crystal will be described.
FIG. 2 is a time chart showing temporal changes in the seed crystal temperature (growth atmosphere temperature), hydrogen flow rate, carrier gas flow rate, and source gas flow rate. A method for manufacturing a silicon carbide single crystal will be described with reference to FIG. The crystal growth temperature of SiC is 2000 ° C. or higher.

  A seed crystal 7 is placed in the vacuum vessel 1. And in the period shown to t1-t5 of FIG. 2, the reaction container 6 is heated by each coil 17a, 17b, and seed crystal temperature (growth atmosphere temperature) is set to 2300 degreeC. In this temperature raising process, argon or helium as a carrier gas is introduced into the vacuum vessel 1 (reaction vessel 6) from the gas introduction pipes 9 and 10 at the timing t2, and purge is performed. At the time of purging, the inside of the reaction vessel 6 is controlled so as to be under a certain pressure with a carrier gas, and the surface of the seed crystal 7 is cleaned by this carrier gas (inert gas). In this way, the surface of the seed crystal 7 is heated in a clean state.

  In FIG. 2, the purge is performed by introducing argon or helium as a carrier gas. Alternatively, as shown in FIG. 3, hydrogen may be introduced at the timing of t2, as shown in FIG. The surface of the seed crystal 7 may be cleaned).

  Further, in the temperature raising process in FIG. 2, since the temperature in the reaction vessel 6 (growth atmosphere temperature) exceeds 1800 ° C., seeds due to excessive escape of Si accompanying generation of SiC sublimation gas from the seed crystal 7. Crystallization of the crystal surface begins to occur. Therefore, supply of hydrogen gas is started at the timing of t3 at a temperature of 1800 ° C. or lower in order to ensure a clean surface. Moreover, supply of source gas (monosilane and propane) is started at the timing of t4. As a result, the seed crystal 7 is prevented from being etched and disappeared against etching of several tens of μm / hour, and the surface of the seed crystal can be protected. In this manner, crystal growth can be performed from the silicon carbide seed crystal 7 with the surface of the silicon carbide seed crystal 7 being a clean surface by the etching gas.

  In this state (while supplying hydrogen and source gas), heating is performed to a crystal growth temperature (2300 ° C.) for producing an ingot while growing SiC on the surface of the seed crystal. That is, as shown in FIG. 4A, the temperature in the reaction vessel 6 is raised to the crystal growth temperature while the crystal (silicon carbide single crystal) 21 is grown on the surface of the seed crystal 7 by supplying the source gas. Crystal defects in the crystal 21 in FIG.

  In FIG. 2, after reaching 2300 ° C., which is the temperature at which the ingot can grow crystals (after t5), the flow rate and ratio of the raw material gases (monosilane and propane) for growing high-quality SiC are increased during the period from t5 to t6. Set.

  After that (at the timing of t6 in FIG. 2), the source gas (monosilane and propane) is supplied while the atmospheric temperature is maintained at the crystal growth temperature, and the flow rate of the etching gas hydrogen is increased so that As shown in FIG. 4B, the crystal 21 grown on the seed crystal surface in the temperature rising process is removed by etching. Specifically, etching is performed using the X-ray source 18 and the camera 19 until the surface of the seed crystal 7 is exposed while checking the etching amount by measuring the thickness of the crystal 21 and the thickness of the seed crystal 7. At this time, for example, the flow rate of the etching gas is controlled as necessary.

  When the surface of the seed crystal 7, that is, the clean surface is exposed (timing at t7 in FIG. 2), the etching gas hydrogen is slowly reduced so that the ambient temperature does not change, or the change in the ambient temperature is minimized. The amount is decreased and this is performed until the timing t8 in FIG. That is, in the period from t7 to t8 in FIG. 2 (etching gas reduction period), the etching gas is gradually reduced while maintaining the ambient temperature at the crystal growth temperature, and the etching gas is changed from etching to growth. Crystal growth is started from the surface of the crystal 7 as shown in FIG. At this time, crystal growth is started on the seed crystal 7 under high quality conditions.

  Note that the etching gas hydrogen may be reduced to such an extent that crystal growth occurs, and is not necessarily zero. The temperature of the etching process is preferably 2100 ° C. or higher at which sublimation is promoted, and the surface can be cleaned by etching in a relatively short time by hydrogen etching assisted by sublimation.

  In the growth step shown in FIG. 4C, the crystal 21 having crystal defects is removed by etching as shown in FIG. 4B, and the growth is performed from the seed crystal 7 having no defects. It becomes. Thereafter, the silicon carbide single crystal 20 of FIG. 4C is grown to the target ingot length, and then the raw material supply is stopped and the crystal is taken out by cooling.

  In this way, a high-quality silicon carbide single crystal can be obtained without being affected by crystal defects in the initial stage of growth caused by temperature changes accompanying the introduction of source gas and deviation from high-quality crystal growth conditions in the temperature rising process or the initial stage of growth. Can be manufactured. In other words, a high-quality silicon carbide single crystal can be grown on the seed crystal without being affected by quality deterioration due to temperature change at the time of supplying the source gas and growth conditions at the time of temperature rise.

  The flow rate change rate of the etching gas affects the generation of crystal defects, and the relationship is shown in FIG. In FIG. 5, the change in growth atmosphere temperature (growth chamber temperature) is taken on the horizontal axis, and the crystal defect density is taken on the vertical axis. From FIG. 5, it can be seen that the rate of change in the flow rate of the etching gas is preferably such that the change in the growth atmosphere temperature (reaction chamber temperature) is 5 ° C. or less per minute. Specifically, since the change rate itself of the etching gas flow rate varies depending on the capability and size of the apparatus, the optimum value may be set for each apparatus.

  In FIG. 2, an etching gas (hydrogen) is supplied in the temperature rising process, and the crystal 21 is grown from the seed crystal 7 by supplying the raw material gas in a state where the surface of the seed crystal 7 is cleaned by the etching gas. . Instead of this, the supply of the etching gas (hydrogen) may be started at the timing of t6 in FIG. In this case, the etching starting from t6 in FIG. 2 after the temperature rise removes the crystal 21 and further removes a predetermined amount of the surface of the seed crystal 7 so that the clean surface is exposed.

As described above, this embodiment has the following features.
When the silicon carbide single crystal 20 is grown from the silicon carbide seed crystal 7 by supplying the source gas (monosilane and propane) to the silicon carbide seed crystal 7 in the crystal growth temperature atmosphere, the following first to third steps are performed. To. First, as the first step, the growth atmosphere temperature is raised to the crystal growth temperature so that the crystal 21 grows from the silicon carbide seed crystal 7 by supplying the raw material gas to the silicon carbide seed crystal 7. Then, as a second step, at least the crystal 21 grown from the silicon carbide seed crystal 7 is removed by the etching gas supplied to the silicon carbide seed crystal 7 in addition to the raw material gas while maintaining the growth atmosphere temperature at the crystal growth temperature. The clean surface of silicon carbide seed crystal 7 is exposed. Further, as the third step, the etching gas supplied in addition to the source gas is gradually reduced while maintaining the growth atmosphere temperature at the crystal growth temperature, and crystal growth is started from the clean surface of the silicon carbide seed crystal 7. .

  Therefore, in the first step, the crystal 21 is formed in the silicon carbide seed crystal 7 without setting the optimum growth condition at the time of temperature rise. In the subsequent second step, the etching is continued with the etching gas supplied in addition to the source gas until the clean surface of the seed crystal is exposed after the temperature rise is completed and high-quality growth can be started. Further, in the subsequent third step, the etching gas is gradually reduced after exposing the clean surface of the seed crystal. As a result, the seed crystal 7 can grow a high-quality silicon carbide single crystal without being affected by the quality deterioration caused by the temperature change at the time of supplying the source gas and the growth condition at the time of temperature rise. That is, it is possible to manufacture a high-quality silicon carbide single crystal by eliminating defects due to crystal defects that occur in the early stage of growth due to the temperature raising process.

  Further, in the first step, the crystal 21 is grown from the silicon carbide seed crystal 7 by supplying the source gas with the surface of the silicon carbide seed crystal 7 being a clean surface (in the case of FIGS. 2 and 3). Therefore, the etching amount of the seed crystal 7 can be made zero.

  Further, the flow rate of the etching gas when the etching gas is gradually reduced is gradually changed so that the change in the atmospheric temperature is 5 ° C./min or less. As a result, the flow rate reduction rate is controlled so that the temperature change accompanying the change in the gas flow rate is 5 ° C./min or less. It becomes possible to grow a quality silicon carbide single crystal.

  In addition, when the crystal 21 grown from at least the silicon carbide seed crystal 7 is removed by the etching gas in the second step and the clean surface of the silicon carbide seed crystal 7 is exposed, the silicon carbide seed is obtained by the X-ray source 18 and the camera 19. The etching amount was controlled while measuring the thickness of the crystal 7 and the thickness of the crystal 21 grown from the silicon carbide seed crystal 7 using X-rays. Thereby, etching is performed while measuring the thickness of the seed crystal 7 and the thickness of the grown crystal 21, thereby preventing the loss of the seed crystal 7 due to excessive etching and the insufficient etching amount due to insufficient supply of the etching gas. The quality at the initial stage of growth can be improved with high reproducibility. Although the etching amount was controlled while measuring the thickness of the silicon carbide seed crystal 7 and the thickness of the crystal 21 using X-rays, only the thickness of the silicon carbide seed crystal 7 or only the thickness of the crystal 21 was controlled. The etching amount may be controlled while measuring using X-rays. That is, the etching amount may be controlled while measuring at least one of the thickness of the silicon carbide seed crystal 7 and the thickness of the crystal 21 grown from the silicon carbide seed crystal 7 using X-rays.

Further, a heat storage member 12 that flows in contact with the etching gas is provided in the etching gas supply passage to the silicon carbide seed crystal 7 in the space to be heated between the gas inlet and the silicon carbide single crystal 20. 12 makes it difficult for the atmospheric temperature to change when the etching gas is reduced. This makes it difficult for crystal defects to occur due to a temperature change caused by a change in the flow rate of the etching gas, which is preferable for growing a high-quality silicon carbide single crystal.
(Second Embodiment)
Next, the second embodiment will be described focusing on the differences from the first embodiment.

FIG. 6 is a time chart in the present embodiment that replaces FIG.
In FIG. 2, the etch back is performed after reaching a certain temperature after the temperature raising process, but in the present embodiment shown in FIG. 6, the etch back is performed in the temperature raising process (a period until the temperature reaches a certain temperature).

explain in detail.
In the temperature raising process (period t1 to t5), purge is performed by flowing argon or helium as a carrier gas at the timing of t2 (starting the supply of the carrier gas). Further, in the temperature raising process, supply of hydrogen gas as an etching gas is started at timing t3 before the atmospheric temperature reaches 1800 ° C. Moreover, supply of source gas (monosilane and propane) is started at the timing of t4. In the temperature raising process, the surface of the seed crystal 7 is slowly etched by hydrogen gas as an etching gas. Specifically, by supplying hydrogen to the seed crystal 7 in addition to the source gas as shown in FIG. 7A, the growth surface of the seed crystal 7 is etched as shown in FIG. 7B. At this time, the etching amount is controlled while the thickness of the silicon carbide seed crystal 7 is measured by the X-ray source 18 and the camera 19 (for example, the flow rate of the etching gas is controlled).

  As described above, in the period from t1 to t5 (temperature raising period) in FIG. 6, the reaction vessel 6 is introduced into the reaction vessel 6 while introducing at least monosilane and propane and the etching gas that exposes the clean surface of the seed crystal 7. The inside is heated up to the crystal growth temperature. As a result, when the crystal growth temperature is reached, the seed crystal surface is exposed in a clean state.

  Then, after reaching the temperature at which the ingot at t5 in FIG. 6 can be produced, the flow rate and the ratio of the source gas for growing high-quality SiC are set in a state where the atmospheric temperature is maintained in the period from t5 to t6.

  Thereafter, the hydrogen gas as the etching gas is slowly reduced while controlling the change in the ambient temperature to be minimal at the timing of t7 in FIG. Here, the hydrogen gas as the etching gas may be reduced to such an extent that crystal growth occurs, and does not necessarily need to be zero. Crystal growth starts on the seed crystal 7 under high quality conditions by reducing the amount of hydrogen gas as the etching gas.

  As described above, during the period from t7 to t8 (etching gas reduction period) in FIG. 6, the etching gas is gradually reduced while maintaining the atmosphere temperature at the crystal growth temperature by controlling the change in the growth atmosphere temperature to be minimum. Then, the crystal growth is started as shown in FIG. 7C from the clean surface of the seed crystal 7 which is changed from etching to growth and exposed by the etching gas. At this time, as shown in FIG. 7B, growth is performed from the seed crystal 7 whose surface is etched to expose the clean surface. Then, after growing the silicon carbide single crystal 20 of FIG. 7C to the target ingot length, the raw material supply is stopped and the crystal is taken out. This eliminates the need for etching until the clean surface of the seed crystal 7 is exposed after the temperature rise as in the first embodiment, and crystal growth can be started by reducing the etching gas immediately after the temperature rise. .

  By following this process, it is possible to manufacture a high-quality silicon carbide single crystal without being affected by the temperature change accompanying the introduction of the source gas and the crystal defects caused by the deviation from the high-quality crystal growth conditions in the temperature rising process. . In other words, a high-quality silicon carbide single crystal can be grown on the seed crystal without being affected by quality deterioration due to temperature change at the time of supplying the source gas and growth conditions at the time of temperature rise.

  Also in this example, the flow rate of the etching gas when the etching gas is gradually reduced during the period from t7 to t8 in FIG. 6 is gradually changed so that the change in the atmospheric temperature is 5 ° C./min or less. It is good to.

  In FIG. 6, the purge is performed by introducing argon or helium as a carrier gas, but instead, as shown in FIG. 8, hydrogen may be introduced at the timing of t <b> 2 (with hydrogen gas). The surface of the seed crystal 7 may be cleaned).

As described above, this embodiment has the following features.
As a first step, the growth temperature of the crystal is grown while etching the surface of the silicon carbide seed crystal 7 with the etching gas supplied to the silicon carbide seed crystal 7 in addition to the source gases (monosilane and propane) to expose the clean surface. Raise to temperature. Then, as a second step, the etching gas supplied in addition to the source gas is gradually reduced while maintaining the growth atmosphere temperature at the crystal growth temperature, and crystal growth is started from the clean surface of the silicon carbide seed crystal 7. . Therefore, in the first step, the etching gas is supplied in addition to the source gas at the time of raising the temperature so that the surface of the seed crystal 7 is etched to expose the clean surface, so that the seed crystal 7 changes in temperature or rises when the source gas is supplied. It is possible to grow a high-quality silicon carbide single crystal without being affected by quality deterioration due to changes in the growth conditions during warming (a high-quality silicon carbide single crystal can be produced).

  Further, when the growth atmosphere temperature is raised to the crystal growth temperature while etching the surface of the silicon carbide seed crystal 7 with the etching gas and exposing the clean surface in the first step, the carbonization is performed by the X-ray source 18 and the camera 19. The etching amount was controlled while measuring the thickness of the silicon seed crystal 7 using X-rays. Since etching is performed while measuring the thickness of the seed crystal 7, it is possible to eliminate the disappearance of the seed crystal 7 due to excessive etching and insufficient etching amount due to insufficient supply of etching gas, and grow with good reproducibility. The initial quality can be made high.

  In the description so far, the gas growth method for supplying the raw material from the outside of the reaction vessel has been described. That is, by disposing the silicon carbide seed crystal 7 in the reaction vessel 6 inside the vacuum vessel 1 and introducing a mixed gas containing at least a Si-containing gas and a C-containing gas into the reaction vessel 6. This was applied when the silicon carbide single crystal 20 was grown from the silicon carbide seed crystal 7. Not only this but also when applied to the sublimation method, it is possible to obtain the same result that the quality at the initial stage of growth can be made high.

  FIG. 9 shows a schematic cross section of a silicon carbide single crystal manufacturing apparatus when applied to the sublimation method. In FIG. 9, a graphite crucible 31 is disposed in a vacuum vessel 30, and a solid material (silicon carbide material) 32 is disposed at the bottom of the bottomed cylindrical graphite crucible 31. A graphite lid 33 is disposed on the upper surface opening of the bottomed cylindrical graphite crucible 31, and a silicon carbide seed crystal 7 is disposed on the lower surface of the graphite lid 33. A vacuum can be drawn from the upper surface of the vacuum vessel 30 by the main pump 34 and the auxiliary pump 35. An RF coil 36 is wound outside the vacuum vessel 30, and the inside of the graphite crucible 31 can be heated by energization of the coil 36. Argon gas and hydrogen gas as an etching gas can be supplied into the vacuum container 30 from the bottom surface of the vacuum container 30.

  Further, in the upper surface opening of the graphite crucible 31, a passage to the hydrogen gas seed crystal 7 is provided between the outer peripheral surface of the graphite lid 33 and the inner peripheral surface of the graphite crucible 31. A heat storage member 37 is disposed. In this way, the heat storage member 37 that flows in contact with the etching gas is provided in the etching gas supply passage to the silicon carbide seed crystal 7 in the space to be heated, and the heat storage member 37 causes the ambient temperature when the flow rate of the etching gas changes. Is difficult to change.

  Then, a sublimation gas is generated from the solid raw material 32 in a crystal growth temperature atmosphere, and this gas (gas used as the raw material) is supplied to the silicon carbide seed crystal 7 to grow the silicon carbide single crystal 20 from the silicon carbide seed crystal 7. . At this time, as described in the first embodiment, the growth atmosphere temperature is set such that the crystal 21 is grown from the silicon carbide seed crystal 7 by supplying the sublimation gas from the solid raw material 32 to the silicon carbide seed crystal 7. The temperature is raised to the crystal growth temperature (first step). Then, at least the crystal 21 grown from the silicon carbide seed crystal 7 is removed by the etching gas supplied to the silicon carbide seed crystal 7 in addition to the sublimation gas from the solid raw material 32 while maintaining the growth atmosphere temperature at the crystal growth temperature. The clean surface of silicon carbide seed crystal 7 is exposed (second step). Further, while maintaining the growth atmosphere temperature at the crystal growth temperature, the etching gas supplied in addition to the sublimation gas from the solid raw material 32 is gradually reduced to start crystal growth from the clean surface of the silicon carbide seed crystal 7. (Third step).

  Alternatively, as described in the second embodiment, the surface of the silicon carbide seed crystal 7 is etched by the etching gas supplied to the silicon carbide seed crystal 7 in addition to the sublimation gas from the solid raw material 32 to obtain a clean surface. While being exposed, the growth atmosphere temperature is raised to the crystal growth temperature (first step). Then, while maintaining the growth atmosphere temperature at the crystal growth temperature, the etching gas supplied in addition to the sublimation gas from the solid raw material 32 is gradually reduced to start crystal growth from the clean surface of the silicon carbide seed crystal 7. (Second step).

The schematic sectional drawing of the manufacturing apparatus of the silicon carbide single crystal in embodiment. The time chart which shows transition of the temperature in the 1st Embodiment, or flow volume. Time chart showing changes in temperature and flow rate. (A)-(c) is sectional drawing which shows the state of a crystal | crystallization. The figure which shows the relationship between a temperature change and a crystal defect density. The time chart which shows transition of the temperature and flow volume in 2nd Embodiment. (A)-(c) is sectional drawing which shows the state of a crystal | crystallization. Time chart showing changes in temperature and flow rate. The schematic sectional drawing of the manufacturing apparatus of the silicon carbide single crystal in the case of applying to a sublimation method. Sectional drawing for demonstrating background art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Vacuum vessel, 6 ... Reaction vessel, 7 ... Silicon carbide seed crystal, 9 ... Mixed gas introduction tube, 10 ... Mixed gas introduction tube, 12 ... Heat storage member, 17 ... Heating coil, 18 ... X-ray source, 19 ... Camera 20 ... silicon carbide single crystal, 21 ... crystal, 30 ... vacuum vessel, 31 ... graphite crucible, 37 ... heat storage member.

Claims (7)

In a method for producing a silicon carbide single crystal, a gas as a raw material is supplied to a silicon carbide seed crystal (7) under a crystal growth temperature atmosphere to grow the silicon carbide single crystal (20) from the silicon carbide seed crystal (7).
A first step of raising the growth atmosphere temperature to the crystal growth temperature so that the crystal (21) grows from the silicon carbide seed crystal (7) by supplying a raw material gas to the silicon carbide seed crystal (7); ,
At least the crystal (21) grown from the silicon carbide seed crystal (7) is removed by the etching gas supplied to the silicon carbide seed crystal (7) in addition to the raw material gas while maintaining the growth atmosphere temperature at the crystal growth temperature. A second step of exposing the clean surface of the silicon carbide seed crystal (7),
While maintaining the growth atmosphere temperature at the crystal growth temperature, the etching gas supplied in addition to the raw material gas is gradually reduced to start crystal growth from the clean surface of the silicon carbide seed crystal (7). 3 steps,
A method for producing a silicon carbide single crystal, comprising: In the first step, the crystal (21) is grown from the silicon carbide seed crystal (7) by supplying the gas as the raw material with the surface of the silicon carbide seed crystal (7) being a clean surface. The method for producing a silicon carbide single crystal according to claim 1. In a method for producing a silicon carbide single crystal, a gas as a raw material is supplied to a silicon carbide seed crystal (7) under a crystal growth temperature atmosphere to grow the silicon carbide single crystal (20) from the silicon carbide seed crystal (7).
The growth atmosphere temperature is raised to the crystal growth temperature while etching the surface of the silicon carbide seed crystal (7) with the etching gas supplied to the silicon carbide seed crystal (7) in addition to the raw material gas to expose the clean surface. A first step of heating;
While maintaining the growth atmosphere temperature at the crystal growth temperature, the etching gas supplied in addition to the raw material gas is gradually reduced to start crystal growth from the clean surface of the silicon carbide seed crystal (7). Two steps,
A method for producing a silicon carbide single crystal, comprising: The flow rate of the etching gas when the etching gas is gradually reduced is gradually changed so that the change in the ambient temperature is 5 ° C./min or less. A method for producing a silicon carbide single crystal according to claim 1. When the crystal (21) grown from at least the silicon carbide seed crystal (7) is removed by the etching gas in the second step to expose the clean surface of the silicon carbide seed crystal (7), the silicon carbide seed crystal (7) The etching amount is controlled while measuring at least one of the thickness of the crystal and the thickness of the crystal (21) grown from the silicon carbide seed crystal (7) using X-rays. The manufacturing method of the silicon carbide single crystal of any one of 1, 2, 4. When the growth atmosphere temperature is raised to the crystal growth temperature while etching the surface of the silicon carbide seed crystal (7) with the etching gas and exposing the clean surface in the first step, the silicon carbide seed crystal (7) The method for producing a silicon carbide single crystal according to claim 3 or 4, wherein the etching amount is controlled while measuring the thickness using X-rays. A heat storage member (12, 37) in which the etching gas flows in contact with the etching gas supply passage to the silicon carbide seed crystal (7) in the space to be heated is provided, and the etching gas is supplied by the heat storage member (12, 37). The method for producing a silicon carbide single crystal according to any one of claims 1 to 6, wherein the ambient temperature is hardly changed when the amount is reduced.

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